CA1151847A - Recovery of aromatics from styrene production off-gas - Google Patents
Recovery of aromatics from styrene production off-gasInfo
- Publication number
- CA1151847A CA1151847A CA000362953A CA362953A CA1151847A CA 1151847 A CA1151847 A CA 1151847A CA 000362953 A CA000362953 A CA 000362953A CA 362953 A CA362953 A CA 362953A CA 1151847 A CA1151847 A CA 1151847A
- Authority
- CA
- Canada
- Prior art keywords
- gas
- aromatics
- absorption oil
- line
- ethylbenzene
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
- C01B3/52—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with liquids; Regeneration of used liquids
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D47/00—Separating dispersed particles from gases, air or vapours by liquid as separating agent
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1487—Removing organic compounds
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C7/00—Purification; Separation; Use of additives
- C07C7/11—Purification; Separation; Use of additives by absorption, i.e. purification or separation of gaseous hydrocarbons with the aid of liquids
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
- C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
- C01B2203/0415—Purification by absorption in liquids
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
- C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
- C01B2203/0465—Composition of the impurity
- C01B2203/048—Composition of the impurity the impurity being an organic compound
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Water Supply & Treatment (AREA)
- General Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Inorganic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Treating Waste Gases (AREA)
- Gas Separation By Absorption (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
Abstract
Abstract of the Disclosure An off-gas from a process for producing styrene from ethylbenzene, which contains non-condensables, in particular hydrogen, as well as some aromatics, in par-ticular ethylbenzene, is contacted with a higher boiling absorption oil to scrub aromatics from the off-gas and provide an off-gas essentially free of aromatics. The absorption step is employed as a final treatment of the off-gas; i.e., subsequent to initial treatment of the off-gas by chilling and/or ethylbenzene scrubbing to ini-tially reduce the aromatics content thereof. A preferred absorption oil is the heavy byproduct obtained from a process for producing ethylbenzene, containing polyethyl-benzenes.
Description
~ 5~ ~ 4 ~
This invention relates ~o the production of styrene, and more particularly to treating an off-gas produced in a process directed to the production of styrene from ethylben-æene.
In the catalytic dehydrogenation of ethylbenzene to produce styrene, the reactor effluent is normally cooled and partially condensed to recover crude styrene product. The off-gas from the cooling and partial condensation, which con-tains primarily hydrogen as the non-condensable, has a high content of aromatic hydrocarbons. In order to reduce such aromatic hydrocarbon losses, such off-gas is generally com-pressed, partially condensed and scrubbed with ethylbenzene, followed by cooling and chilling to thereby reduce the aro-matic content. In such processes, however, the vapors, which contain as major components hydrogen, methane and carbon diox-ide, are saturated with water and aromatic hydrocarbons;
namely, ethylbenzene. Such aromatics represent an important loss of feedstock.
The present invention is directed to treating the off-gas from a process directed to producing styrene from ethylbenzene in order to provide an off-gas essentially free of aromatic hydrocarbons.
In particular, the present invention provides a pro-cess for treating an off-gas generated in a process for pro-ducing styrene from ethylbenzene, said off-gas containing hydrogen and aromatic hydrocarbons, which comprises finally treating the off-gas which contains from 0.5% to 10% by volume of aromatic hydrocarbons by contacting the off~gas at a tem-pPrature of from 35F. to 125F. and a pressure of from 15 to 100 psia with an absorption oil for aromatics having a 5-volume percent distillation temperature of at lPast 400F.
t~
to absorb aromatic hydrocarbons present in the of-gas, an~ providing a remaining off-gas essentially free of aromatic hydrocarbons, which contains less than 0.2%, by volume, of aromatic hydrocarbons and recovering aromatic hydrocarbons absorbed by the absorption oil.
In accordance with the present invention, the off-gas from the process for producing styrene from ethylben-zene is finally treated with a heavier oil which absorbs aromatics to thereby provide a remaining off-gas which is essentially free of aromatic hydrocarbons.
The oil for absorbing aromatic hydrocarbons has a 5-volume percent distillation temperature of at least 400F, with the 5-volume percent distillation tem-perature generally being at least 600F.
-la-~5~ 7 . .
In most cases, the 95-volume percent distillation temperature does not exceed about 1000F. The abss~rption oil may be any one o~ a wi~lc variety of absorption oils which are kno~rn 'o be effective for absorbing aromatics such as ethylbenzene, with such absorption oil being characterizecl by thc 5 5-volume percent boiling characteristics hereinabove noted. In most cases, the absorption oils which are effective for absorbing aromatics are of an aromatic nature, although such absorption oiLs may contain some aliphatic components. As representative e~amples of suitable absorption oils, there may be mentioned gas oils, fluid catalytic 10 cracking cycle oils, lube oil extraction raffinates and the like. A pre-ferred absorption oil is the heavy byproduct from the process for pro-ducing ethylbenzene by alkylation of benzene. Such heavy byproduct generally contains as principal components polyethylbenzenes and diphenylethane.
The off-gas which is subjected to scrubbing with the heavier absorption oil has an aromatics content of from 0. 5 to about 10-volume percent, with the other principal components being hydrogen, methane, water vapor and carbon dioxide. The aromatics present in the off-gasareprincipally comprised of ethylbenzene and the off-gas may 2G further include one or more of benzene, toluene and styrene.
The scrubbing with the heavier absorption oil is employed as a final treatment of the off-gas in order to essentially eliminate aromatics therefrom. Consequently, prior to contact with the heavier absorption oil, the off-gas has been tréated to reduce the aromatic content thereof 25 by one or more of chilling and¦or ethylben~ene scrubbing.
The invention will be further described with respect to preferred -- embodiments thereof illustrated in the accompanying drawings, whcrein:
Figure 1 is a simplified schematic fLow diagram of a prefcrred embodiment of the present invention;
Figure 2 is a simplified schematic flow diagram of a modifi-cation of the embodiment of Figure 1; and Figure 3 is a simplified schematic flow diagram of a urther modification of the embodiment of Figure 1.
Referring now to IFigure 1 of the drawings~ ethylbenzene fresh feed, in line 10, and a further portion OI ethylbenzene fresh feed, including absorbed aromatics, in line 11, obtained as hereinafter described,are introduced into a styrene production zone, generally designated as 12 wherein the ethylbenzene is catalytically dehydrogenated to produce styrene, by a procedure known in the art. As known in the art, the feed to zone 12 generally also includes steam. In general, the styrene production is operated at a temperature in the order of from 500F to 1500FJ and at a pressu--e in the order of from 2 to 25 psia.
~ styrene production effluent is withdrawn from the styrene production zone 12 through line 14 and introduced into a suitable cooling zorle, schematically generally indicated as 15 (which may contain onc or more cooling stages) in orcler to cool the effluent gas and conclense crude styrene product, which contains in add ition to styrene, ethy l-.
benzene~ and one or more of toluene and benzene. Crude styrene product is withdrawn from cooling zone 15, through line 16 for intro-duction into a separation and recc)very zone (not shown).
Uncondensed gas, which is at a temperature in the order of from 60F to 150F, and at a pressure of from 2 to 25 psia, is with-drawn from cooling zone 15 through line 20, and such gas contains hydrogen, methàne, carbon dioxide, as welL as water vapor ancl aro-matics, (ethylbenzene and some styrene and/or toluene and/or benzene).
The gas in line 16 is compressed by the use of a compressor, sche-matically generally indicated as 17, and the compressed gas in line 18 is introduced into a cooling zone, schematically generally indicated as 19, which may contain one or more cooling stages in order to reduce the temperature of the gas and condense aromatics therefrom. Condensed aromatics are recovered frorn cooling zone 19 through line 21, and are combined with the crude product in line 16 for introduction into the styrene separation and recovery zone (not shown).
The remaining gas withdrawn from the cooling zone 19 through line 22, which is generally at a temperature in the order of from 75F
to 125~F, and at a pressure in the order of from 15 ~o 100 psia and which still contains aromatics, is introduced into a scrubbing zone, generally indicated as 23, wherein the gas is countercurrently contacted with a portion of the ethylbenzene freshfeed to the styrene production, intro-duced through line 24. The scrubber 23 contains suitable meansJ in order to increase gas-liquid contact~ e. g. packing 25, and as a result of such contact, further aromatics are scrubbed from the gas.
~51B47 Ethylbenzene, containing absorbed aromatics, is withdrawn from scrubber 25 through line 11 for introduction into the styrenc production zone 12.
The gas ~vithdrawn from scrubber 23 through Line 27 is 5 at a temperature in the order of from 35F to 150F, and a pressure in the order of from 15 to 100 psia. Such gas still contains some aromatics, and in general, as hereinabove described/ the aromatic content of the gas is in the order of from 0. 5% to 10%, by volume.
The gas in line 27 is introduced into a further scrubber 28, which includes suitable gas-liquid contacting means, shown as bed 29 wherein the gas is contacted wLth an absorption oil int:roduced through line 31. The absorption oil introduced through line 31 is a heavy oil of the type hereinabove described, which is effective for absorbing aromatic hydrocarbons from the gas introduced through Line 27. As hereinabove described, the absorption oil is preferahly the heav~T by-product from a process for producing ethylbenzene, ~nd is characterized by a 5-volume percent distillation temperature of at least 400F, preferably at least 6û0:F, and a 95~volume percent distillation tem-perature of no greater than 1000F.
The scrubber 28 is operated at conditions to remove essentially alL of the aromatics present in the gas introduced through line 27; i.e.
the aromatic content of the scrubbed gas is less than 0. 5%,most generally less than 0 . 2~o and preferably less than 0. 05~, all by volume.
In general, scrubber 28 is operated at a temperature in the order of from 35F to 125F, and a pressure in the order of from 15 to 100 psia.
. . .
~n off-gas, essentially free of aromatic hydrocarbons, which generally contains 90-volume percent or more of hydrogen, is re-covered from scrubber 28 through linc 32. Such oîf-gas may be burned, or in some cases, may be further treated to recover hydrogcn therefrom.
Rich absorption oil withdrawn from scrubber 28 through line 33 is heated in exchangers 34 and 35 prior to being introducetl through line 36 into an absorption oil stripper, schematically generally Incli-cated as 37, with the stripper being provkled with suitable gas-Liquid contacting means, such as a bed 38.
Stripper 37 is operated at temperatures and pressures to strip absorbed aromatics from the absorption oil, with the stripper 37 pre-ferably beiIlg operated by the use of a suitable stripping gas., such as steam, provided through line 39. Although steam is preferred" it is to be understood that stripping gases other than steam may also be employed. Thus, for example, Instead vf steam, there may be used:
nitrogen, methane, carbon dioxide or the like. The stripping gas can be a combination of the above. It is also to be understood that the stripper may be operated without a stripping gas, although this is less preferred. ALternatively, the stripper may be replaced with a flash drum when higher boiling absorption oils are used.
In general, stripper 37 is operated at a temperature in the order of from 125~F to 300~F, and at a pressure in the order of from 1 to 25 psia.
Stripped arornatic components are withdrawn from stripper 37 through line 41, and such stripped components are introduced into the cooling zone 15 to condense such aromatics for recovery with the crude product in line 1fi. It is to be understood that the stripped aromatics can be condensed in a separate zone, although condensation 5 in zone 15 is preferred.
Lean absorption oil is withdrawn from stripper 3rt through line 42, and a portion thereof is purged through line 43, with the re-maining portions being cooled in exchanger 3D~, by indirect heat transfer with rich absorption oil, and further cooled in exchanger 40, prior to 10 introduction into scrubber 28 through line 31. Suitable make-up absorption oil is provided through line 44.
Thus, in accordance with the embodiment, the off-gas from the styrene production, which still contains some aro~ tic hydrocarbons, is finally treated with a heavier absorption oil to recover such aromatic 15 hydrocarbons for ultimate reuse in the process.
Referring to Figure 2 of the drawings, there is shown a modi-fication of the embodiment described with respect to Figure 1. Thus~
in accordance with the embodiment of ~igure 2, off-gas from cooling stage 19, which is in line 229 is cooled in a chiller, schematically 20 generally indicated as 101, to condense a portion of the aromatics contained therein, wi~h the condensed portion being recovered in line 102 for introduction into the crude styrene recovery system ~not shown), or in the alternative to the styrene production reactor.
The uncondensed portion of the gas9 in line 103, which is generally at a temperature in the order of from 32F to 100DF" and at a pressure in the order of from about 15 to 100 psia is introduced -- into scrubber 104, including suitable gas-liquid contact means9 in the form of a bed 105. In scrubber 104, the gas is contacted with a heavy absorption oil, of the type hereinabove described introducecl 5 through line 130 for absorbing aromatics which remaLn in the gas introduced through line 103. The scrubber 104 is operated at con-ditions to produce a gas which is esserltially free of aromatics (as hereinabove described), with the essentially aromatics free gas, ~vhich primarily contains hydrogen and methane, being recovered through 10 line 105 for further processing by burning or hydrogen recovery, as hereinabove described.
The scrubber 104 is generally operated at a temperature in the order of from 35F to 125F, and at a pressure in the order of from 15 to 100 psia.
Rich absorption oil is withdrawn from scrubber 104 through line 106 and heated in exchangers 107 and 108 prior to introduction thereof into a str ipp ing column 1 0 9 through line 110, The s tr ipp ing column 109 is provided with suitable gas liquid corltact means, for example, a packed bed 112. The stripper 109 is provided with a 20 suitable stripping gas, such as steam~ through line 114; however, as hereinabove described with respect to the embodiment of Figure 1, other stripping gases could be used, or in the alternative, the stripper could be operated without the use of a stripping gas or replaced with a flash drum. The stripper 109 is operated to strip absorbed aromatics 25 from the absorption oil, with the stripped aromatics being witlldrawn .
from stripper 109 through line 115 for introduction into the cooling zone 15, as hereinabove described with respect to the embodimcnt of Figure 1, or in the alternative condensed separately. In gencral, the stripper is operated at a temperature in the order of from 125F to 300F, and at a pressure in the order of 1 to 25 psia.
Lean absorption o il is withdrawn from str ipper 1 0 9 through line 116, with a portion thereof being purged through line 117. Lean absorption oil is then cooled in exchanger 107 by indirect heat transfer with rich absorption oil, and further cooled in exchanger 118 prior to introduction into the scrubber 104. Make-up absorption oil is provided through line 121.
Thus, in accordance with the embodiment of Figure 2, the ethyl-benzene scrubber has been eliminated, and replaced by a chillerJ with the off-gas being finally treated, as hereinabove described with respect to the embodiment of Figure 1 by use of a heavier absorption oil in order to provide an off-gas which is essentially free of aromatics.
A further modification of the embodiment of Figure 1 is shown in Figure 3 of the drawings. Referring to Figure 3, off-gas in line 22 is introduced into the ethylbenzene scrubber 23?, which includes suitable gas-liquid contact bed 251J wherein the gas is countercurrently contacted with ethylbenzene, as an absorption liquid, introduced through line 24'.
The scrubber 23t is operated as hereinabove described with respect to the embodiment of Figure 1, with the ethylbenzene, containing absorbed aromatics being recovered therefrom through line 11 ' for recycle to the styrene production.
~53 ~39L7 . . .
The gas withdrawnfrom scrubber 23' through line 201, which is generally at a temperature in the order of from 35 to 150F
and a pressure in the order of from about 15 to 100 psia, is coole~l in exchanger 202, and further chilled in chiller 203 in order to condense 5 further aromatics from the gas, with the condensed aromatics bcing withdrawn from exchanger 202 through line 204 and from chiller 203 through line 205 The condensed aromatics recovered through lines 204 and 205 are recycled to the styrene production reactor or in the alternative to the recovery system. The gas withdrawn from chiller 203 through line 206, which is at a temperature in the order of from 32F to 100F, and at a pressure in the order of from about 15 to 100 psia is heated in exchanger 202 by indirect heat transfer with the gas in line 201, and the heated gas in line 207 is introduced into an additional scrubber 208, which includes suitable gas-liquid contact 1 5 means in the form of a bed 2 09 wherein the gas is countercurrently contacted with absorption oil introduced through line 211 for absorbing aromatics. The absorption oil employed in line 211 is a heavier ab-sorption oil of the type hereinabove described. The scrubber 208 is operated at conditions to absorb essentially all of the aromatics present in the gas introduced through line 207, with a gas, essentially free of aromatics, as hereinabove described, being recovered -frorn scrubber 208 through line 209 for burning and/or hydrogen recovery as herein-above described. In general, the scrubber 208 is operated at tempe-rature in the order of from 35F to 125F, and at a pressure Ln the order of from 15 to 100 psia.
4'7 Rich absorption oil withdrawn from scrubber 208 throu~h line 212 is heated in exchangers 214 and 215, with the heated rich absorption oil in line 216 being introduced into a stripper 217, whicll includes suitable gas-liquid contacting means such as a bed 218. Thc stripper 218 is preferably providecl with a stripping gasJ such as steam through lLne 219, although, as hereinabove described, other stripping gases may be employed or the stripper 217 may be operated without a stripping gas or replaced with a flash drum. The strippcr 217 is operated at conditions to strip absorbed aromatics from the absorption oil, with the stripped aromatics being withdrawn from the stripper Z17 through line 221 for introduction into the cooling section 15 as hereinabove described with respect to Figure 1, or in the alter-native condensed separately. In general, stripper 217 is operated at temperatures in the order of from 125~F to 300F, and at a pressure in the order of from 1 to 25 psia.
Lean absorption oil is withdrawn from stripper 217 through line 222 and a portion thereof is purged through line 22S. The lean absorption oil is cooled in exchanger 214 by indirect heat transfer with the rich absorption oil in line 212, and is further cooled in exchanger 230 prior to introduction into the absorption column 208 through line 211.
Make-up absorption oil is provided ~hrough line 216.
Thus, in accordance with the embodiment of Figure 3, prior to the final treatment with the heavier absorption oil, and subsequent to ethylben~ene scrubbing, the gas is cooled to condense additional aromatics therefrom.
- . ~
1l~5~B47 Although the invention has been particularly described witl respect to embodiments thereof as illustrated in the accompanying drawings, it is to be understood that the invention may be practised other than as particularly described with respect to the embodimcnts.
5 Thus, for example, the various heat transfer stages may be effecte(l other than as particularly described.
The present invention is particularly advantageou;, in that it is possible to recover essentially all of the aromatics which are present in l;he off-gas generated in a styrene production process. The increased 10 recovery of aromatics improves the economics of the process. In addition, if hydrogen is to be recovered from the off~gas, by increasing the hydrogen concentration, such hydrogen recovery is enhanced.
_ 12 ~
This invention relates ~o the production of styrene, and more particularly to treating an off-gas produced in a process directed to the production of styrene from ethylben-æene.
In the catalytic dehydrogenation of ethylbenzene to produce styrene, the reactor effluent is normally cooled and partially condensed to recover crude styrene product. The off-gas from the cooling and partial condensation, which con-tains primarily hydrogen as the non-condensable, has a high content of aromatic hydrocarbons. In order to reduce such aromatic hydrocarbon losses, such off-gas is generally com-pressed, partially condensed and scrubbed with ethylbenzene, followed by cooling and chilling to thereby reduce the aro-matic content. In such processes, however, the vapors, which contain as major components hydrogen, methane and carbon diox-ide, are saturated with water and aromatic hydrocarbons;
namely, ethylbenzene. Such aromatics represent an important loss of feedstock.
The present invention is directed to treating the off-gas from a process directed to producing styrene from ethylbenzene in order to provide an off-gas essentially free of aromatic hydrocarbons.
In particular, the present invention provides a pro-cess for treating an off-gas generated in a process for pro-ducing styrene from ethylbenzene, said off-gas containing hydrogen and aromatic hydrocarbons, which comprises finally treating the off-gas which contains from 0.5% to 10% by volume of aromatic hydrocarbons by contacting the off~gas at a tem-pPrature of from 35F. to 125F. and a pressure of from 15 to 100 psia with an absorption oil for aromatics having a 5-volume percent distillation temperature of at lPast 400F.
t~
to absorb aromatic hydrocarbons present in the of-gas, an~ providing a remaining off-gas essentially free of aromatic hydrocarbons, which contains less than 0.2%, by volume, of aromatic hydrocarbons and recovering aromatic hydrocarbons absorbed by the absorption oil.
In accordance with the present invention, the off-gas from the process for producing styrene from ethylben-zene is finally treated with a heavier oil which absorbs aromatics to thereby provide a remaining off-gas which is essentially free of aromatic hydrocarbons.
The oil for absorbing aromatic hydrocarbons has a 5-volume percent distillation temperature of at least 400F, with the 5-volume percent distillation tem-perature generally being at least 600F.
-la-~5~ 7 . .
In most cases, the 95-volume percent distillation temperature does not exceed about 1000F. The abss~rption oil may be any one o~ a wi~lc variety of absorption oils which are kno~rn 'o be effective for absorbing aromatics such as ethylbenzene, with such absorption oil being characterizecl by thc 5 5-volume percent boiling characteristics hereinabove noted. In most cases, the absorption oils which are effective for absorbing aromatics are of an aromatic nature, although such absorption oiLs may contain some aliphatic components. As representative e~amples of suitable absorption oils, there may be mentioned gas oils, fluid catalytic 10 cracking cycle oils, lube oil extraction raffinates and the like. A pre-ferred absorption oil is the heavy byproduct from the process for pro-ducing ethylbenzene by alkylation of benzene. Such heavy byproduct generally contains as principal components polyethylbenzenes and diphenylethane.
The off-gas which is subjected to scrubbing with the heavier absorption oil has an aromatics content of from 0. 5 to about 10-volume percent, with the other principal components being hydrogen, methane, water vapor and carbon dioxide. The aromatics present in the off-gasareprincipally comprised of ethylbenzene and the off-gas may 2G further include one or more of benzene, toluene and styrene.
The scrubbing with the heavier absorption oil is employed as a final treatment of the off-gas in order to essentially eliminate aromatics therefrom. Consequently, prior to contact with the heavier absorption oil, the off-gas has been tréated to reduce the aromatic content thereof 25 by one or more of chilling and¦or ethylben~ene scrubbing.
The invention will be further described with respect to preferred -- embodiments thereof illustrated in the accompanying drawings, whcrein:
Figure 1 is a simplified schematic fLow diagram of a prefcrred embodiment of the present invention;
Figure 2 is a simplified schematic flow diagram of a modifi-cation of the embodiment of Figure 1; and Figure 3 is a simplified schematic flow diagram of a urther modification of the embodiment of Figure 1.
Referring now to IFigure 1 of the drawings~ ethylbenzene fresh feed, in line 10, and a further portion OI ethylbenzene fresh feed, including absorbed aromatics, in line 11, obtained as hereinafter described,are introduced into a styrene production zone, generally designated as 12 wherein the ethylbenzene is catalytically dehydrogenated to produce styrene, by a procedure known in the art. As known in the art, the feed to zone 12 generally also includes steam. In general, the styrene production is operated at a temperature in the order of from 500F to 1500FJ and at a pressu--e in the order of from 2 to 25 psia.
~ styrene production effluent is withdrawn from the styrene production zone 12 through line 14 and introduced into a suitable cooling zorle, schematically generally indicated as 15 (which may contain onc or more cooling stages) in orcler to cool the effluent gas and conclense crude styrene product, which contains in add ition to styrene, ethy l-.
benzene~ and one or more of toluene and benzene. Crude styrene product is withdrawn from cooling zone 15, through line 16 for intro-duction into a separation and recc)very zone (not shown).
Uncondensed gas, which is at a temperature in the order of from 60F to 150F, and at a pressure of from 2 to 25 psia, is with-drawn from cooling zone 15 through line 20, and such gas contains hydrogen, methàne, carbon dioxide, as welL as water vapor ancl aro-matics, (ethylbenzene and some styrene and/or toluene and/or benzene).
The gas in line 16 is compressed by the use of a compressor, sche-matically generally indicated as 17, and the compressed gas in line 18 is introduced into a cooling zone, schematically generally indicated as 19, which may contain one or more cooling stages in order to reduce the temperature of the gas and condense aromatics therefrom. Condensed aromatics are recovered frorn cooling zone 19 through line 21, and are combined with the crude product in line 16 for introduction into the styrene separation and recovery zone (not shown).
The remaining gas withdrawn from the cooling zone 19 through line 22, which is generally at a temperature in the order of from 75F
to 125~F, and at a pressure in the order of from 15 ~o 100 psia and which still contains aromatics, is introduced into a scrubbing zone, generally indicated as 23, wherein the gas is countercurrently contacted with a portion of the ethylbenzene freshfeed to the styrene production, intro-duced through line 24. The scrubber 23 contains suitable meansJ in order to increase gas-liquid contact~ e. g. packing 25, and as a result of such contact, further aromatics are scrubbed from the gas.
~51B47 Ethylbenzene, containing absorbed aromatics, is withdrawn from scrubber 25 through line 11 for introduction into the styrenc production zone 12.
The gas ~vithdrawn from scrubber 23 through Line 27 is 5 at a temperature in the order of from 35F to 150F, and a pressure in the order of from 15 to 100 psia. Such gas still contains some aromatics, and in general, as hereinabove described/ the aromatic content of the gas is in the order of from 0. 5% to 10%, by volume.
The gas in line 27 is introduced into a further scrubber 28, which includes suitable gas-liquid contacting means, shown as bed 29 wherein the gas is contacted wLth an absorption oil int:roduced through line 31. The absorption oil introduced through line 31 is a heavy oil of the type hereinabove described, which is effective for absorbing aromatic hydrocarbons from the gas introduced through Line 27. As hereinabove described, the absorption oil is preferahly the heav~T by-product from a process for producing ethylbenzene, ~nd is characterized by a 5-volume percent distillation temperature of at least 400F, preferably at least 6û0:F, and a 95~volume percent distillation tem-perature of no greater than 1000F.
The scrubber 28 is operated at conditions to remove essentially alL of the aromatics present in the gas introduced through line 27; i.e.
the aromatic content of the scrubbed gas is less than 0. 5%,most generally less than 0 . 2~o and preferably less than 0. 05~, all by volume.
In general, scrubber 28 is operated at a temperature in the order of from 35F to 125F, and a pressure in the order of from 15 to 100 psia.
. . .
~n off-gas, essentially free of aromatic hydrocarbons, which generally contains 90-volume percent or more of hydrogen, is re-covered from scrubber 28 through linc 32. Such oîf-gas may be burned, or in some cases, may be further treated to recover hydrogcn therefrom.
Rich absorption oil withdrawn from scrubber 28 through line 33 is heated in exchangers 34 and 35 prior to being introducetl through line 36 into an absorption oil stripper, schematically generally Incli-cated as 37, with the stripper being provkled with suitable gas-Liquid contacting means, such as a bed 38.
Stripper 37 is operated at temperatures and pressures to strip absorbed aromatics from the absorption oil, with the stripper 37 pre-ferably beiIlg operated by the use of a suitable stripping gas., such as steam, provided through line 39. Although steam is preferred" it is to be understood that stripping gases other than steam may also be employed. Thus, for example, Instead vf steam, there may be used:
nitrogen, methane, carbon dioxide or the like. The stripping gas can be a combination of the above. It is also to be understood that the stripper may be operated without a stripping gas, although this is less preferred. ALternatively, the stripper may be replaced with a flash drum when higher boiling absorption oils are used.
In general, stripper 37 is operated at a temperature in the order of from 125~F to 300~F, and at a pressure in the order of from 1 to 25 psia.
Stripped arornatic components are withdrawn from stripper 37 through line 41, and such stripped components are introduced into the cooling zone 15 to condense such aromatics for recovery with the crude product in line 1fi. It is to be understood that the stripped aromatics can be condensed in a separate zone, although condensation 5 in zone 15 is preferred.
Lean absorption oil is withdrawn from stripper 3rt through line 42, and a portion thereof is purged through line 43, with the re-maining portions being cooled in exchanger 3D~, by indirect heat transfer with rich absorption oil, and further cooled in exchanger 40, prior to 10 introduction into scrubber 28 through line 31. Suitable make-up absorption oil is provided through line 44.
Thus, in accordance with the embodiment, the off-gas from the styrene production, which still contains some aro~ tic hydrocarbons, is finally treated with a heavier absorption oil to recover such aromatic 15 hydrocarbons for ultimate reuse in the process.
Referring to Figure 2 of the drawings, there is shown a modi-fication of the embodiment described with respect to Figure 1. Thus~
in accordance with the embodiment of ~igure 2, off-gas from cooling stage 19, which is in line 229 is cooled in a chiller, schematically 20 generally indicated as 101, to condense a portion of the aromatics contained therein, wi~h the condensed portion being recovered in line 102 for introduction into the crude styrene recovery system ~not shown), or in the alternative to the styrene production reactor.
The uncondensed portion of the gas9 in line 103, which is generally at a temperature in the order of from 32F to 100DF" and at a pressure in the order of from about 15 to 100 psia is introduced -- into scrubber 104, including suitable gas-liquid contact means9 in the form of a bed 105. In scrubber 104, the gas is contacted with a heavy absorption oil, of the type hereinabove described introducecl 5 through line 130 for absorbing aromatics which remaLn in the gas introduced through line 103. The scrubber 104 is operated at con-ditions to produce a gas which is esserltially free of aromatics (as hereinabove described), with the essentially aromatics free gas, ~vhich primarily contains hydrogen and methane, being recovered through 10 line 105 for further processing by burning or hydrogen recovery, as hereinabove described.
The scrubber 104 is generally operated at a temperature in the order of from 35F to 125F, and at a pressure in the order of from 15 to 100 psia.
Rich absorption oil is withdrawn from scrubber 104 through line 106 and heated in exchangers 107 and 108 prior to introduction thereof into a str ipp ing column 1 0 9 through line 110, The s tr ipp ing column 109 is provided with suitable gas liquid corltact means, for example, a packed bed 112. The stripper 109 is provided with a 20 suitable stripping gas, such as steam~ through line 114; however, as hereinabove described with respect to the embodiment of Figure 1, other stripping gases could be used, or in the alternative, the stripper could be operated without the use of a stripping gas or replaced with a flash drum. The stripper 109 is operated to strip absorbed aromatics 25 from the absorption oil, with the stripped aromatics being witlldrawn .
from stripper 109 through line 115 for introduction into the cooling zone 15, as hereinabove described with respect to the embodimcnt of Figure 1, or in the alternative condensed separately. In gencral, the stripper is operated at a temperature in the order of from 125F to 300F, and at a pressure in the order of 1 to 25 psia.
Lean absorption o il is withdrawn from str ipper 1 0 9 through line 116, with a portion thereof being purged through line 117. Lean absorption oil is then cooled in exchanger 107 by indirect heat transfer with rich absorption oil, and further cooled in exchanger 118 prior to introduction into the scrubber 104. Make-up absorption oil is provided through line 121.
Thus, in accordance with the embodiment of Figure 2, the ethyl-benzene scrubber has been eliminated, and replaced by a chillerJ with the off-gas being finally treated, as hereinabove described with respect to the embodiment of Figure 1 by use of a heavier absorption oil in order to provide an off-gas which is essentially free of aromatics.
A further modification of the embodiment of Figure 1 is shown in Figure 3 of the drawings. Referring to Figure 3, off-gas in line 22 is introduced into the ethylbenzene scrubber 23?, which includes suitable gas-liquid contact bed 251J wherein the gas is countercurrently contacted with ethylbenzene, as an absorption liquid, introduced through line 24'.
The scrubber 23t is operated as hereinabove described with respect to the embodiment of Figure 1, with the ethylbenzene, containing absorbed aromatics being recovered therefrom through line 11 ' for recycle to the styrene production.
~53 ~39L7 . . .
The gas withdrawnfrom scrubber 23' through line 201, which is generally at a temperature in the order of from 35 to 150F
and a pressure in the order of from about 15 to 100 psia, is coole~l in exchanger 202, and further chilled in chiller 203 in order to condense 5 further aromatics from the gas, with the condensed aromatics bcing withdrawn from exchanger 202 through line 204 and from chiller 203 through line 205 The condensed aromatics recovered through lines 204 and 205 are recycled to the styrene production reactor or in the alternative to the recovery system. The gas withdrawn from chiller 203 through line 206, which is at a temperature in the order of from 32F to 100F, and at a pressure in the order of from about 15 to 100 psia is heated in exchanger 202 by indirect heat transfer with the gas in line 201, and the heated gas in line 207 is introduced into an additional scrubber 208, which includes suitable gas-liquid contact 1 5 means in the form of a bed 2 09 wherein the gas is countercurrently contacted with absorption oil introduced through line 211 for absorbing aromatics. The absorption oil employed in line 211 is a heavier ab-sorption oil of the type hereinabove described. The scrubber 208 is operated at conditions to absorb essentially all of the aromatics present in the gas introduced through line 207, with a gas, essentially free of aromatics, as hereinabove described, being recovered -frorn scrubber 208 through line 209 for burning and/or hydrogen recovery as herein-above described. In general, the scrubber 208 is operated at tempe-rature in the order of from 35F to 125F, and at a pressure Ln the order of from 15 to 100 psia.
4'7 Rich absorption oil withdrawn from scrubber 208 throu~h line 212 is heated in exchangers 214 and 215, with the heated rich absorption oil in line 216 being introduced into a stripper 217, whicll includes suitable gas-liquid contacting means such as a bed 218. Thc stripper 218 is preferably providecl with a stripping gasJ such as steam through lLne 219, although, as hereinabove described, other stripping gases may be employed or the stripper 217 may be operated without a stripping gas or replaced with a flash drum. The strippcr 217 is operated at conditions to strip absorbed aromatics from the absorption oil, with the stripped aromatics being withdrawn from the stripper Z17 through line 221 for introduction into the cooling section 15 as hereinabove described with respect to Figure 1, or in the alter-native condensed separately. In general, stripper 217 is operated at temperatures in the order of from 125~F to 300F, and at a pressure in the order of from 1 to 25 psia.
Lean absorption oil is withdrawn from stripper 217 through line 222 and a portion thereof is purged through line 22S. The lean absorption oil is cooled in exchanger 214 by indirect heat transfer with the rich absorption oil in line 212, and is further cooled in exchanger 230 prior to introduction into the absorption column 208 through line 211.
Make-up absorption oil is provided ~hrough line 216.
Thus, in accordance with the embodiment of Figure 3, prior to the final treatment with the heavier absorption oil, and subsequent to ethylben~ene scrubbing, the gas is cooled to condense additional aromatics therefrom.
- . ~
1l~5~B47 Although the invention has been particularly described witl respect to embodiments thereof as illustrated in the accompanying drawings, it is to be understood that the invention may be practised other than as particularly described with respect to the embodimcnts.
5 Thus, for example, the various heat transfer stages may be effecte(l other than as particularly described.
The present invention is particularly advantageou;, in that it is possible to recover essentially all of the aromatics which are present in l;he off-gas generated in a styrene production process. The increased 10 recovery of aromatics improves the economics of the process. In addition, if hydrogen is to be recovered from the off~gas, by increasing the hydrogen concentration, such hydrogen recovery is enhanced.
_ 12 ~
Claims (8)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for treating an off-gas generated in a process for producing styrene from ethylbenzene, said off-gas containing hydrogen and aromatic hydrocarbons, which comprises: finally treating the off-gas which contains from 0.5% to 10% by volume of aromatic hydro-carbons by contacting the off-gas at a temperature of from 35°F. to 125°F. and a pressure of from 15 to 100 psia with an absorption oil for aromatics having a 5-volume percent distillation temperature of at least 400°F. to absorb aromatic hydrocarbons present in the off-gas, providing a remaining off-gas essentially free of aromatic hydrocar-bons, which contains less than 0.2%, by volume, of aromatic hydrocarbons and recovering aromatic hydrocarbons absorbed by the absorption oil.
2. The process of Claim 1,wherein prior to the final treatment the off-gas is scrubbed with ethylbenzene to re-duce the aromatic content of the off-gas.
3. The process of Claim 1,wherein prior to the final treatment, the off-gas is chilled to recover aromatics by condensation.
4. The process of Claim 1,wherein prior to the final treatment, the off-gas is scrubbed with ethylbenzene and chilled to reduce the aromatic content thereof.
5. The process of Claim 1, wherein the absorption oil has a 95-volume percent distillation temperature of no greater than 1000°F.
6. The process of Claim 5, wherein the absorption oil has a 5-volume percent distillation temperature of at least 600°F.
7. The process of Claim 6, wherein the absorption oil is the heavy byproduct from the production of ethyl-benzene which is comprised of polyethylbenzenes and diphenyl-ethane.
8. The process of Claim 1, wherein the aromatic hydrocarbons are recovered from the absorption oil by strip-ping.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/094,672 US4288234A (en) | 1979-11-15 | 1979-11-15 | Recovery of aromatics from styrene production off-gas |
| US94,672 | 1979-11-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1151847A true CA1151847A (en) | 1983-08-16 |
Family
ID=22246486
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000362953A Expired CA1151847A (en) | 1979-11-15 | 1980-10-22 | Recovery of aromatics from styrene production off-gas |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4288234A (en) |
| JP (1) | JPS6033412B2 (en) |
| KR (1) | KR830001368B1 (en) |
| CA (1) | CA1151847A (en) |
| DE (1) | DE3042824A1 (en) |
| FR (1) | FR2469390A1 (en) |
| GB (1) | GB2063291B (en) |
| IT (1) | IT1146997B (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4479025A (en) * | 1982-11-22 | 1984-10-23 | Uop Inc. | Alkylaromatic hydrocarbon dehydrogenation process |
| US4708721A (en) * | 1984-12-03 | 1987-11-24 | General Signal Corporation | Solvent absorption and recovery system |
| JPH0437046Y2 (en) * | 1986-07-18 | 1992-09-01 | ||
| US5004862A (en) * | 1988-06-27 | 1991-04-02 | Hildinger Henry W | Process for recycling and purifying condensate from a hydrocarbon or alcohol synthesis process |
| US6388155B1 (en) * | 2000-08-01 | 2002-05-14 | Abb Lummus Global Inc. | Styrene dehydrogenation reactor effluent treatment |
| ITMI20052514A1 (en) * | 2005-12-29 | 2007-06-30 | Polimeri Europa Spa | IMPROVED PROCEDURE FOR DEHYDROGENATION OF ALCHILAEOMATIC HYDROCARBONS INTENDED FOR THE PRODUCTION OF VINYLAROMATIC MONOMERS |
| EP2067749A1 (en) | 2007-11-29 | 2009-06-10 | Total Petrochemicals France | Process for purification of an aqueous phase containing polyaromatics |
| EP2065355A1 (en) | 2007-11-29 | 2009-06-03 | Total Petrochemicals France | Process for cooling the stream leaving an ethylbenzene dehydrogenation reactor |
| US8999257B2 (en) * | 2009-09-22 | 2015-04-07 | Fina Technology, Inc. | Offgas stream direct contact condenser |
| FR2974363B1 (en) * | 2011-04-22 | 2014-12-19 | Michelin Soc Tech | RECOVERY OF MONOMERS. |
| NL2018908B1 (en) | 2017-05-12 | 2018-11-15 | Stichting Energieonderzoek Centrum Nederland | Production and isolation of monocyclic aromatic compounds from a gasification gas |
| US20240026231A1 (en) * | 2022-07-22 | 2024-01-25 | T.En Process Technology, Inc. | Systems and methods for enhancing the recovery of styrene |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2729588A (en) * | 1952-02-23 | 1956-01-03 | Fluor Corp | Operating a reboiler system for fractionating absorber-stills which comprises separately introducing vapors and liquid from the reboiler into the still and mixing absorbed vapors vaporized from the still bottoms with the liquid before its introduction into the still |
| US2959626A (en) * | 1957-07-15 | 1960-11-08 | Cosden Petroleum Corp | Process for the production of styrenegrade ethyl benzene |
| US3412171A (en) * | 1966-06-27 | 1968-11-19 | Petro Tex Chem Corp | Purification of hydrocarbons |
| JPS5637227B2 (en) * | 1972-06-20 | 1981-08-29 | ||
| JPS5439385B2 (en) * | 1972-06-20 | 1979-11-27 | ||
| US3963575A (en) * | 1974-02-25 | 1976-06-15 | A. E. Staley Manufacturing Company | Producing pullulanase with organisms having a superior capacity to elaborate pullulanase |
| DD114251A1 (en) * | 1974-10-16 | 1975-07-20 |
-
1979
- 1979-11-15 US US06/094,672 patent/US4288234A/en not_active Expired - Lifetime
-
1980
- 1980-10-22 CA CA000362953A patent/CA1151847A/en not_active Expired
- 1980-11-10 GB GB8036057A patent/GB2063291B/en not_active Expired
- 1980-11-12 KR KR1019800004337A patent/KR830001368B1/en active
- 1980-11-12 IT IT50142/80A patent/IT1146997B/en active
- 1980-11-13 JP JP55160627A patent/JPS6033412B2/en not_active Expired
- 1980-11-13 DE DE19803042824 patent/DE3042824A1/en active Granted
- 1980-11-13 FR FR8024122A patent/FR2469390A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| US4288234A (en) | 1981-09-08 |
| DE3042824C2 (en) | 1988-02-04 |
| GB2063291A (en) | 1981-06-03 |
| JPS5690023A (en) | 1981-07-21 |
| IT1146997B (en) | 1986-11-19 |
| FR2469390A1 (en) | 1981-05-22 |
| KR830001368B1 (en) | 1983-07-19 |
| DE3042824A1 (en) | 1981-05-27 |
| FR2469390B1 (en) | 1983-12-30 |
| IT8050142A0 (en) | 1980-11-12 |
| GB2063291B (en) | 1983-09-07 |
| KR830004187A (en) | 1983-07-06 |
| JPS6033412B2 (en) | 1985-08-02 |
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